Disruption of fuel supplies due to fighting between rebel groups in northern Syria is threatening the closure of hospitals and paralysing the work of ambulances and rescue services, an international medical charity said today.

A US-based human rights group accused the Syrian government on Tuesday of launching aerial attacks that have killed or injured thousands of civilians in the past 11 months of the country's four-year civil war.

Islamic State militants holed up in the Qalamoun mountains on the Syrian-Lebanese border are seeking to gain control of nearby Lebanese villages to support their fighting positions, the head of Lebanon's main security apparatus told Reuters.

Syrian President Bashar Assad made a rare public appearance on Saturday by attending prayers for a key Muslim holiday at a mosque in the capital, Damascus, hours after the US-led coalition carried out new airstrikes against Islamic State group militants in Syria.

Eighteen foreign fighters from the Islamic State, including an American jihadist, were killed in a Syrian air raid on a town near the militant group's main stronghold city of Raqqa in eastern Syria, a human rights monitoring group said on Thursday.

For the first time in the Syrian civil war, al-Qaida fighters are hunkered down on Israel's doorstep, and Israelis in the lush, hilly Golan Heights who have long considered Syrian President Bashar Assad their bitter foe are now worried about something more ominous - that they could become the militants' next target.

The Syrian rebels that the US now wants to support are in poor shape, on the retreat from the radical al Qaeda breakaway group that has swept over large parts of Iraq and Syria, with some rebels giving up the fight. It is not clear whether the new US promise to arm them will make a difference.

The four main host countries for Syrian refugees said at a meeting on Sunday that only the wider distribution of aid inside Syria could curb an exodus that is putting huge strains on neighbouring states.

For three years, residents of Syria's Mediterranean provinces have watched from their coastal sanctuary as civil war raging further inland tore the country apart, killing tens of thousands of people and devastating historic cities.